Method of cold-drawing metal



Patented Jan. 2, 1945 @UNlTED STATES, PATENT OFFICE 4 METHOD OF COLD-DRAWING METAL Harley A. Montgomery, Highland Park, Mich.

No Drawing. Application May 25, 1942,

' Serial No. 444,402

7 Claims.

This invention relates to an improved drawing compound and method usable in deep drawing and other metal forming operations wherein metal is drawn or formed through or between dies to desired configurations, and further to an like lubricants into the body of which is preferably incorporated a fortifying substance of a solid nature. Fortifying substances which are commonly used are soaps of alkaline or non-alkaline metals, finely divided graphite, calcium carbonate, white lead or other similar elements and materials which may be termed film fortifiers.

The purpose of the addition of film fortifiers is to improve the pressure withstanding proper-' ties of the lubricating medium; the object being to prevent intimate contact of the work piece with the die during the process of the deforming of the metal under high pressures.

In metal forming and drawing operations, the lubricating film including its fortifier, if a fortifier is employed, is often termed the interface film." The more indestructible and adherent the interface film employed the lesserw'ill be the tendency to score or scratch during the cold drawing operations.

Many types of interface films have been investigated. Several have been found to be extremely efiicient and, effective. Among those which are commonly used are lead or copper plated films. Also, non-metallic films which are often employed are pure soap films, oxidized oil films and thermo-setting films which depend metallic coatings, are not sufilciently indestructible and do not wholly prevent scratching, scoring and galling of the relatively soft metal work piece by the relatively harder metal die. However, prior art soft metal coatings such as those formed by electro-plating, hot dipping and the like are generally too expensive.

The primary object of the instant invention is to provide for use in cold drawing, forming and other metal configurating operations a, method of depositing an indestructible interface film, which is practical and economical to apply, the

said film being equal in efiiciency to those pre:

viously formed by electrolytic methods, and surpassing in action any of the non-metallic films now generally employed.

During the many experiments conducted which preceded the instant invention, the performance and chemistry of the so-called extreme pressure lubricants have been carefully reviewed. It has been found that such lubricants are not particularly efiicient in preventing the difficulties encountered in cold drawing operations offerrous metals if they are applied at the moment of or just previous to the cold drawing operations.

The applicant herein has discovered that those types of extreme pressure lubricants which contain sulphur possess superior merit as lubricants for cold drawing purposes if, and only unless, their application to the work piece is done in a manner which admits of a comparatively long elanseof time between application of the lubricant and the cold drawing of the metal.

.This phenomenon has been analyzed in close detail and to it the applicant has attributed the formation of an oxide film on the surface of the treated metals. On further investigation it was found that the said oxide film is not necessarily a pure oxide film, but rather, a complex sulfide and oxide film.

a The foregoing sulphide-oxide film phenomena has long been supposed to exist, by various researchers in sulphur bearing oilylubricants and recently has been confirmed in literature. Reference is had to a paper entitled Extreme pressure lubricants, published in the November, 1941, issue of Industrial and Engineering Chemistry,

page 1352, sub-topic "Discussion of sulphur oils. from which the following quotations are made:

(a) The results of various treatments of iron with sulphur oil are consistent in that all showed surface phases of some iron hydroxide and iron oxide. The oxides are not those which would be formed by exposure of iron to air at room ternperature and consequently were a result of treatment." I

(b) "Although only iron oxides were observed on iron surfaces treated with sulphur oils, it is possible that iron sulfide was formed and escaped detection."

(c) it should be pointed out that there is a eutectic mixture of iron and ferrous sulfide containing about 15 per cent iron whose melting point is about 550 0. below that of iron. If therefore the sulphur attacks the iron surface to form a sulfide, there may be a tendency for eutectic melting to take place at the iron-ferrous sulfide interface under the action of high loads and high temperatures. This process would result in chemical polishing in a manner quite similar to that advanced in the case of the iron phosphide. Whether this action is an important property of sulphur oils is not certain, but it seems possible that it may be."

(d) Free sulphur oils can withstand high loads despite high friction and high operating temperatures. The formation of iron oxide both by the direct oxidation of iron and by the oxidation of iron sulfide may account for this characteristic. The oxides with their comparatively high melting points provide good anti-welding agents to prevent galling. At the same time they have a mildabrasive action Practically all efforts of other experimenters have been exerted in the direction of bearing lubrication. These developments have little significance upon the use of the sulphide-oxide film phenomena for the purpose of cold drawing of ferrous metals, because in the performance of such operations, the work pieces, under the time element of conventional handling during production, cannot possibly realize the maximum benefit of the sulphide-oxide film forming phenomena. This, as pointed out, is due to the momentary period of time between application of lubricant and the cold drawing process. Essentially the problem is to apply a substantial interface film to the work piece. This cannot be accomplished with commonly marketed sulphur bearing lubricants under normal methods employed in the cold drawing of ferrows metals.

The object of the inventor is to apply more or less instantaneously to the surfaces of metal work pieces a substantially indestructible interface film so as to obtain a substantial coating quickly of a nature similar to that described in the cited reference. Experiments clearly confirmed that ferrous metal oxidized by sulphur bearing lubricants is of a particular nature inasmuch as ferrous surfaces oxidized in atmosphere at various temperatures did not show enhanced cold drawing properties. The applicant then had for the object of his development the problem of applying, in a short interval of time, a substantially indestructible interface film of a nature similar to that obtained in long periods of time by the association of sulphur bearing lubricants with ferrous bodies.

The supposition is that, during the association of sulphur bearing oils with ferrous bodies, there is initially a heavy film of ferrous sulphide formed on the ferrous body, which film is then gradually converted from the outside toward the ferrous body into iron hydroxide or iron oxide, the latter action being due in greater part to dissolved oxygen. However, not all of the original ferrous sulphide isconverted into the oxide, and, it is behaved that the innermost portion of the film which originally coated the asperities of the metal remains .to form a eutectic alloy which, because of its low melting point, forms a mobile resultant coating may be defined as an interface film composed of an oxide class coating which includes iron oxide, sulphide oxide, iron hydroxide, hydrated iron'oxide or any combination of them and an overlying film of an oleaginous material.

The applicant has discovered that an extremely heavy substantially indestructible interface film employable in ferrous metal forming drawing and other configurating operations is produced when the working surface of a ferrous part is exposed to the chemical action of a compound, whose composition for the most part is an oleaginous material to which has been added sulphur and a minor amount of water. The sulphur may be chemically combined or intimately mixed with the oleaginous material and may exist in concentrations from one-half of one per cent to fifteen per cent. may vary between one-half of one per cent to five per cent, the water, acting as an accelerator of the chemical reaction, and is considered an essential ingredient in the process of instantaneous formation of the protective sulfide oxide film. The oleaginous material employed may be any oily or grease-like substance in natural or artificial combination with sulphur, and the sulphur radical may exist in any organic compound or as elemental sulphur.

It is believed that the water accelerator acts as an oxygen bearing carrier and catalyzes the oxidation which is essential to satisfactory and rapid forming of the desired substantially indestructible interface film on a ferrous metal part. Ferrous metal parts immersed in compositions herein revealed are immediately attacked through chemical action which is evidenced by a readily visible discoloration which ranges in color from a deep blue to dense black. Ferrous metal parts subjected to reaction in a similar non-water bearing lubricant do not develop any visible discoloration and do not possess interface film qualities which function satisfactorily under extreme pressure of drawing, forming or other metal configurating operations. 0n the other hand when ferrous metal parts are immersed in compositions disclosed herein, the parts so treated become more or less instantly coated with a substantially indestructible interface film and may then be successfully cold drawn with equal or improved facility to like metal parts coated with fortified lubricants, expensive plated coatings, or the like.

It has been found preferable to maintain compositions embodying the invention at a temperature from F. to F. during the immersion of the ferrous metal parts therein, at which temperatures, the coating of the ferrous metal parts with the desired interface film is substantially instantaneous, that is, the coating occurs within few seconds to one minute.

The herein disclosure of the drawing compound and method of providing an improved and highly suitable and satisfactory interface film on ferrous metal objects for the purpose of enabling the same to be drawn in or between dies under extreme pressure drawing, forming or other metal configurating operations is employed as illustrative of the invention only, and it is not intended that the said disclosure be construed in a limit- The concentration of water ing sense or in an manner in degradation to the broad scope of the invention as defined by the appended claims.

I claim: 1. In the art of cold drawing ferrous metals, the steps of immersing said metal in a bath composed of an 'oleaginous material, sulphur and water until a heavy black iron sulphide'coating has formed thereon, and then removing said met- 'al from said bath and subjecting said coated metalto a drawing operation.

2. The method of preparing ferrous metals for cold drawing comprising the immersion of said ferrous metal into a bath composed of an oleaginous material, sulphur and water while the said bath is elevated to a temperature from 125 F. to 160 F., and then withdrawing said metal from said bath only after said bath has reacted with said metal to produce a dense black iron sulfide coating thereon.

. 3. In cold drawing of ferrous metals, the steps of forming thereon an interface film by subjecting a ferrous metal to a composition elevated to a temperature from 125 F. to 160 F. composed a of an oleaginous material, sulphur and water wherein the sulphur and water is present in the proportions of from 1% to 20% of the composition and in which composition not less than /z% or more than 5% of sulphur is employed, and

thereafter subjecting said metal to a, drawing operation between dies.

4. In the cold drawing of ferrous metals the steps of forming thereon a composite interface film composed of a class of coatings which consists of iron oxide, iron sulfide, iron hydroxide, hydrated iron oxide, any one or any combination of them, overlaying said interface film. with a film of oleaginous lubricating substance whereby to admit of subsequently cold drawing the ferrous metal under extremely high pressures encountered in modern metal configurating operations, and thereafter subjecting said metal to a drawing operation.

5. In the cold drawing of ferrous metals the steps of forming thereon prior to said drawing operation. an interface film composed of ironsulfide and overlaying said interface film with a film of an oleaginous lubricating substance and then subjecting said metal to a drawing operation.

6. In the cold drawing of ferrous metals the steps of forming thereon an interface film composed of iron sulfide and iron oxide and overlaying said interface film with a film of an oleaginous lubricating substance and then subjecting said metal to a drawing operation.

7. In the art of drawing ferrous metals, the

step of creating a film of iron sulfide of appreciable thickness on said metal prior to the. drawing operation for the purpose of forming an interfacial film during a subsequent drawing operation. anti then subjecting said metal to a drawing operation.

HARLEYA. MONTGOMERY. 

